The present invention concerns novel polyurethane (PUR)-adhesives that, due to good antenna-values (antenna impedance) and insulation resistance in combination with good mechanical properties and reduced blister formation tendency, are especially well suited for the direct glazing of carpanes with integrated antennas.
The requirements that adhesives for the direct glazing in vehicle manufacturing have to meet are steadily extended such that an adhesive has to fulfill several functions. One important additional property consists in that the adhesive for the assembly of vehicle panes with integrated antenna shall not affect the radio reception, and a further additional property consists in that contact corrosion shall be eliminated by the adhesive.
Today an adhesive that is suitable for the application in connection with antennas, i.e. an adhesive with good antenna impedance, and that has low conductivity can only be achieved by drastic reduction of the conductive fillers (e.g. carbon black). This, however, results in that the optimal adaptation of the rheological properties, in particular the non-sagging, as well as the achievement of good mechanical properties is limited, since the rheological as well as the mechanical properties depend from the kind and amount of the fillers.
The impedance problem on which the invention is based can be described as follows:
Panes carrying simultaneously antennas (antenna panes) comprise conductor structures that are in the panes or on the surface of the panes. Said antenna conductors are guided to the border of the panes, in order to be connected with the cables starting from said place. Said connections and bus bars at the borders of the panes can by chance or by intent come into contact with the adhesive used for the panes or said connections and bus bars can entirely be covered with said adhesive. By the adhesive, an additional impedance to the mass is formed, that is observed as blind component and active component. This results in a weaker received power. On the other hand, this also favours the oscillation transfer from the vehicle body to the antenna resulting in back ground noise.
Description of impedance: 
The above presented scheme describes the basic situation. (RKS represents: resistance (R) caused by the adhesive, in a series arrangement as model).
The antenna is loaded with the impedance ZK caused by the adhesive and the impedance of the system itself (conductors) ZL. By the additional impedance ZK caused by the adhesive, the available signal voltage is reduced. This results in a worse received power.
For the impedance two equivalent-circuit diagrams are possible that both are applied. The parallel arrangement with the factors RKP and CKP, or the series arrangement with the factors RKS and CKS.
Said models can be converted into one another.
The impedance thus can be described by a resistance (R) and a capacity (C). Resistance and capacity are dependent on the frequency.
Between said factors the following relations exist:       R    KS    =                              R          KP                          1          +                                    ω              2                        ⁢                          C              KP              2                        ⁢                          R              KP              2                                          ⁢              xe2x80x83            ⁢      and      ⁢              xe2x80x83            ⁢              C        KS              =          xe2x80x83        ⁢                  1        +                              ω            2                    ⁢                      C            KP            2                    ⁢                      R            KP            2                                                ω          2                ⁢                  C          KP                ⁢                  R          KP          2                    
whereby xcfx89 represents the angular frequency (=2xcfx80*frequency).
The two factors (RKP and CKP) or the factors deduced from said factors are now calculated in the automobile producing industry and are determined as standard values for adhesives to be used on panes, in particular wind screens (direct glazing adhesives).
The goal of the present invention thus was to provide adhesives that, without any reduction of the amount of conductive fillers, guarantee good antenna impedance and low conductivity in combination with high mechanical properties, and that are therefore very well suited for the joining of base metals and direct glazing.
Hence, it is a general object of the invention to provide an adhesive that comprises at least one filler (filler comprising adhesive), said adhesive comprising a prepolymer consisting of a polycarbonate prepolymer with a polycarbonate polyol radical having an average equivalence weight (molecular weight per OH-group in the polyol) of about 100 to about 1000, in particular about 250 to about 750, more preferred about 250 to about 500, or from a prepolymer mixture containing a respective polycarbonate prepolymer.
Said compositions can be one-component (1C) compositions or two-component (2C) compositions, and said compositions are especially well suited for the application close to or on antennas.